Hitherto, as an image information compressing method, a feature extracting and coding method of separating image information every pattern included in the image information into two pieces of feature data, and encoding each feature data, thereby compressing the image information is known. An example of the image information compressing method using the feature extraction and coding is disclosed by Johnson K. Yan and David J. Sakrison, “Encoding of Images Based on a Two-component Source Model”, IEEE Transaction on Communications, Vol. COM-25, No. 11 (1977). According to the method, first, cubic root intensity u(x, y)=[i(x, y)]1/3 is obtained from one-dimensional original data i(x, y) converting from original image data by raster scan. The cubic root intensity u(x, y) is separated to a non-continuous component d(x, y) and the remaining component r(x, y) by smoothing, and each of the components is encoded.
In this case, an edge component and a contrast component of the image are included in the non-continuous component d(x, y), and a texture component of the image is included in the remaining component r(x, y), so that the original image is separated into feature components, and each of the feature components is optimally encoded.
However, in the conventional image information compressing method, a spectrum of the one-dimensional original data obtained by raster scan includes many high frequency components. Consequently, at the time of smoothing the one-dimensional original data, the edge component and the contrast component are not sufficiently converted by a smoothing function, but remain as the remaining components. Therefore, sufficiently high coding efficiency cannot be obtained. If the information of the remaining components is reduced in order to increase the coding efficiency, a problem occurs such that deterioration on an image increases.
An object of the present invention is to provide an image information compressing method capable of effectively separating an image into feature components and achieving higher coding efficiency with little deterioration in picture quality in an image information feature separating and coding method.